It is well known to provide liquid fabric conditioning compositions which soften in the rinse cycle.
Such compositions comprise less than 7.5% by weight of softening active, in which case the composition is defined as “dilute”, from about 7.5% to about 30% by weight of active in which case the compositions are defined as “concentrated” or more than about 30% by weight of active, in which case the composition is defined as “super-concentrated”.
Concentrated and super-concentrated compositions are desirable since these require less packaging and are therefore environmentally more compatible than dilute or semi-dilute compositions.
A problem frequently associated with concentrated and superconcentrated compositions, as defined above, is that the product is not stable, especially when stored at high temperatures. Instability can manifest itself as a thickening of the product upon storage, even to the point that the product is no longer pourable.
The problem of thickening upon storage is particularly apparent in concentrated and superconcentrated fabric softening compositions comprising an ester-linked quaternary ammonium fabric softening material having one or more fully saturated alkyl chains.
A further problem known to affect concentrated and super-concentrated fabric softening compositions comprising an ester-linked quaternary ammonium fabric softening material having one or more fully saturated alkyl chains is that the initial viscosity of a fully formulated composition can be very high, up to a point that the composition is substantially unpourable.
However, it is desirable to use ester-linked compounds due to their inherent biodegradability and to use substantially fully saturated quaternary ammonium fabric softening compounds due to their excellent softening capabilities and because they are more stable to oxidative degradation (which can lead to malodour generation) than partially saturated or fully unsaturated quaternary ammonium softening compounds.
Of the types of ester-linked quaternary ammonium materials known, it is desirable to use those based on triethanolamine which produce at least some mono-ester linked component and at least some tri-ester linked component since the raw material has a low melting temperature which enables the manufacturing process of the composition to occur at low temperatures. This reduces difficulties associated with high temperature handling, transport and processing of the raw material and compositions produced therefrom.
It is further desirable to incorporate a perfume into fabric conditioning compositions in order to provide a pleasing aroma when dispensing the product, as well as on wet fabrics treated with the product and on dry fabrics thereafter.
However, a problem commonly encountered when incorporating perfumes into fabric treatment compositions is instability of the product both initially and upon storage.
It is believed that this is because perfumes often contain a wide range of ingredients some of are incompatible with the other ingredients therein. In particular, it is believed that this is because perfumes contain a wide range of ingredients some of which interact with the softener active material to induce phase (structural) changes leading to product viscosity instability.
The problem of instability in fabric conditioning compositions due to perfume has previously been addressed in various ways.
U.S. Pat. No. 5,447,644 discloses a means of controlling the liquid viscosity of rinse conditioner compositions by mixing perfume with a surfactant having an HLB greater than 12 and then adding this to a base.
EP-A1-658616 discloses a method for fragrancing rinse conditioner composition liquids having improved stability by premixing perfume with a high HLB polyethoxylated alcohol or cholesterol.
EP-A1-466235 discloses incorporating perfume into a detergent product by combining the perfume with one or more nonionic emulsifiers to form a structured emulsion.
WO-A1-01/46360 discloses a method of improving the viscosity stability upon storage of a fabric softening composition comprising (a) 0.5% to 30% by weight of at least one ester-linked quaternary ammonium fabric softening compound, (b) perfume, and (c) an alkoxylated nonionic surfactant by the inclusion in the composition of at least one oily sugar derivative in a weight ratio of softening compound to sugar derivative in the range 30:1 to 1:1.